Impact of Elevated CO2 and Temperature On Cotton Growth, Physiology and Biochemistry

Two cultivars (DP16 and 71BRF) of cotton were grown from seed in a sunlit glasshouse for 5 weeks under well-watered, high nutrient conditions exposed to two atmospheric [CO2] (400 ppm and 640 ppm) and two air temperature (Ambient and Amb +4C) treatments. Our objectives were to assess the impact of different climate change scenarios on vegetative growth and physiological performance. In general, the recently developed cultivar (71BRF) exhibited higher rates of photosynthesis, lower total biomass, and greater carbohydrate storage available for boll formation than the older cultivar (DP16). Overall, elevated [CO2] stimulated photosynthesis by 40% while marginally reducing stomatal conductance, thereby substantially increasing water use efficiency (WUE); elevated temperature did not affect these parameters. Importantly, across a VPD range of 1-4 kPa, elevated [CO2] plants had substantially higher WUE than ambient [CO2] plants. Dark respiration was increased 15-20% in higher temperature, but not affected by [CO2] treatment. In general, photosynthetic capacity (Amax, Vcmax and Jmax) was increased by growth in elevated temperature but not elevated [CO2]. Vegetative growth, including mass production and leaf area, was increased 20% in elevated [CO2], but 80-180% in elevated temperature, highlighting the significant role of temperature in regulating plant development. Surprisingly, there were no significant CO2 x temperature interactions. Leaf samples are currently being analysed for gene expression and metabolite profiling. Experiments are also underway to assess the impact of variable soil moisture within the context of CO2 x Temperature experiments in the glasshouse, and subsequent field trials under variable temperature and rainfall conditions in Texas and Narrabri NSW to further assess cotton performance under climate change conditions.